* when a i8086 reference uses only one register, choose it from the set [BX,BP,SI,DI] as it can be treated either as a base or an index, depending on what's convenient

git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@25183 3ad0048d-3df7-0310-abae-a5850022a9f2